板状Cu-Al-Mn形状記憶合金素子の座屈特性に及ぼす繰返し座屈変形の影響

Abstract

The shape memory alloy (SMA) element that shows superelastic behavior exbibits negative stiffness during post-buckling deformation. Buckling deformation recover during unloading due to the shape memory effect. Thus, the negative stiffness region can be used continuously by the buckling of the shape memory alloy. The continuous availability of a negative stiffness region makes it possible to fabricate a passive vibration isolation mechanism with a quasi-zero stiffness structure composed of the combination of SMA elements and regular spring. Therefore, we devised and fabricated the passive vibration isolator using tape-shaped Ti-Ni SMA elements, and this isolator shows the excellent vibration characteristic. However, the physical properties of the Ti-Ni alloy strongly depend on the environmental temperature, which makes the operating temperature range of this vibration isolator very narrow. In this study, we focused on Cu-Al-Mn SMA with lower temperature dependence than Ti-Ni SMA and investigated their buckling characteristics and fatigue characteristics to evaluate their performance as vibration isolators. From the experimental results, it is considered that Cu-Al-Mn SMA exhibits favorable vibration-isolation properties over a wide environmental temperature range because of its smaller temperature dependence of buckling property and smaller stress hysteresis compared to Ti-Ni SMA. However, Cu-Al-Mn SMA has tendency of rapid decrease in reaction force after tens of thousands of cycles of buckling deformation fracturing shortly thereafter. This fracture was caused by intergranular fracture at the position where tensile stress is applied due to buckling deformation.